The voltage stability of large scale renewable energy grid-connected system plays a major role in a power system environment. Nowadays, Integration of large scale wind power may have severe impacts on the power system operation. Stable, reliable and economic operation of the power system under the massive integration of wind power is a big challenge to power system operators. This paper seeks to study the voltage stability problems for the integration of wind power and Photovoltaic (PV) to the IEEE-14 bus network. Modern analytical tools are demonstrated to study voltage stability analysis by using PV analysis and dynamic analysis. Comparative study is developed to present the behavior of voltage stability of the system that employs PV and different types of wind farms. These analyses define the amount of reactive power required to enhance voltage stability. Simulation of 14-IEEE network with integrated renewable energy sources is developed using PSS/E.

In this paper, a direct power predictive controller (DPPC) is derived for a current source inverter (CSI) based single stage photovoltaic (PV) system. The equations of the dynamics, including AC and DC filters, are formulated directly for the PV power and for the active and reactive power injected in the grid. Then, the prediction equations are synthesized straight for the power, and, at each time instant, the optimal switching vector that guarantees simultaneously the control of the power generated by the PV arrays, and the control of the reactive power in the connection to the grid is chosen. This approach aims to guarantee fast and accurate tracking of the power. The proposed system is then validated through simulation and experimental results, showing that the PV system is able to follow the power references, guaranteeing a fast response to a step in the power, and decoupled active and reactive power control, with minimum total harmonic distortion (<5%) of the currents injected in the grid.

Induction generators are the most popular in wind energy conversion system due to its simplicity and absence of synchronization problem. However the major drawback of this machine is its additional reactive burden on the electric network. This paper studies the voltage stability of wind farms (WFs) Connected to IEEE 14 bus network during system disturbances such as a load change, three phase fault or island condition. Those disturbances have a great impact on the system voltages and frequency. A static synchronous compensator (STATCOM) is proposed to maintain voltage and frequency within grid codes requirements. The proposed system shows an excellent performance it maintains the voltage and frequency constants by injection controllable reactive power during system disturbances. MATLAB/SIMULINK and the Power System Analysis Toolbox (PSAT) package are used for the simulation.

Author(s): Erhab Youssef , Rasha M El Azab, Amr M Amin